Botulinum Toxin for Spasmodic Dysphonia (Laryngeal Dystonia): Double Blind Placebo Controlled Assessment of Dose and Technique. Spasmodic dysphonia (SD) and laryngeal dystonia are clinical terms used to describe an action- induced dysphonia resulting from a laryngeal motion disorder. Most cases represent manifestations of primary dystonia, but some are secondary to other neurological entities. Current estimates suggest 15,000-25,000 affected individuals in this country. Because dystonic movements and resulting postures are often unusual, and the condition is rare, it is one of the most frequently misdiagnosed neurological conditions; many patients are referred to psychiatrists for treatment because the correct diagnosis is not made when the individual initially presents for treatment. The diagnosis of dystonia and SD in particular, rests upon the identification of characteristic clinical abnormalities. During the past decade, researchers have made advances in the diagnosis and treatment of the condition; we have begun to assess the genetics. Although local injections of Botox have been reported as a safe and efficacious form of therapy for adductor SD, there has been no formal double-blind study examining the clinical efficacy in treating the phonatory characteristics. Controversy exists regarding dose, and route of injection (unilateral vs. bilateral injections). We initiated treatment of SD with local injections of Botox in 1984 and have treated over 275 patients; the benefit has been dramatic. Over the 6 year interval, we have perfected the technique of injection into both vocal folds with small doses of toxin. We have had an excellent response administering 2.5 U/cord; adverse experiences include excessive breathiness and mild, clinically insignificant, transient aspiration. We have decreased the dose to 1.25 U/cord, and appear to have a similarly good response. It ia important to evaluate alternative treatment programs (unilateral vs. bilateral injections) and dose effects (1.25 vs. 2.5U/cord). In order to make statements and recommendations for clinical care for an exceptionally disabling condition, we need to formally compare these 2 doses and 2 techniques for benefit, and incidence and severity of adverse experiences. We propose a double blind placebo controlled study to assess the efficacy of unilateral injections of 30 Units v. bilateral injections of 2.5 U/cord and 1.25 U/cord. The primary response efficacy variable will be percent of normal function as perceived by the patient with secondary response variables of duration of clinical benefit, voice quality on the Unified Spasmodic Dysphonia Rating Scale, percent of normal as rated by the trained observer, the patient's self assessment rating, visual rating of degree of adductor spasms, electromyographic changes, and also adverse experiences.